The hearing into the attack has now concluded in Manchester and a report from the chairman is expected later this year.
Lawyers for the security services said it was “deep and profound” to regret that suicide bomber Salman Abedi was able to carry out his plot on May 22, 2017.
Cathryn McGahey QC, representing the Home Office, said MI5 was determined to do all it could to protect the public from future atrocities.
But she also defended the security services against allegations of “missed opportunities” to arrest the suicide bomber, heard during the 196-day public hearing, which began in September 2020.
Inquiry chairman Sir John Saunders will write reports indicating whether the attack could or should have been prevented, the planning and preparation by the bomb conspirators, Salman and his brother Hashem.